Originally Posted by Al1943

That's a fairly big change but may not require a longer chain. Put the new cassette on, on a work stand try shifting gently into the big chainring/big cog combination. Check to make sure the rear derailleur has not reached its maximum forward travel (bottomed out). Good to go.
While you're at it check the chain for stretch with a good steel ruler. A 24 pin interval of new chain will be exactly 12 inches in length. When any 24 pin interval measures 12 1/16th inches you need a new chain.

Al